16 ms·

Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

umvi 6y ago
So, according to this paper 34.2-47.5% of US citizens need immunity before the pandemic can be declared over? So best case scenario we can achieve herd immunity with roughly 100M infections/recovered. USA is currently at ~8M infections/recovered, so that means we are roughly 8% of the way to herd immunity (best case). At the current rate of +50K infections per day, that's 20 days per 1M infections, so we need 20 days * 92 = 5 years before we achieve herd immunity (best case, assuming no vaccines)? That doesn't seem right.
- deleted 6y ago
  [deleted]
- zwischenzug 6y ago
  Actual infection count is probably far higher than 8M, isn't it? That's just number of positive tests.
  - seanalltogether 6y ago
    I thought I remembered reading early on that icelandic testing was showing that 50% of all people infected there showed no symptoms. Then add on how many people show symptoms but its not severe enough to get tested.
    - StevePerkins 6y ago
      Well, then add on the number of people who just don't get a test regardless. My child had a fever a few weeks ago, it was an ORDEAL finding a place to get him tested. You have to be quite motivated. If you're not sick enough to require hospitalization, and especially if you're un-insured and poor and don't want to pay a couple-hundred bucks out of pocket, then you'll probably just ride it out and never get tested. I'm sure this is the state of things for tens of millions of Americans.
      - learc83 6y ago
        >My child had a fever a few weeks ago, it was an ORDEAL finding a place to get him tested. You have to be quite motivated. That's because the test won't change anything. If it's positive, they'll tell you to isolate your kid. If it's negative, there's a high enough false negative rate that you'll still need to basically treat them like they have COVID (stay home and isolate).
        AstralStorm 6y ago
        Incorrect. Not being treated early is likely a main factor between likelihood of medium to severe.vs no to mild symptoms, beyond immunity. And isolation of sick patient from viral reservoir (such as fomites and other asymptomatic sick) is known to be important too, as it changes the viral inoculum dose.
        learc83 6y ago
        Normal healthy children who don't develop a severe case aren't treated at all, so talking about early treatment is irrelevant. I literally just talked about this with a close family member who is a Children's ER doctor. >And isolation of sick patient from viral reservoir (such as fomites and other asymptomatic sick) is known to be important too, as it changes the viral inoculum dose. This isn't known to be important. If a person has been infected long enough that they are already symptomatic then "viral inoculum dose" is irrelevant.
    - war1025 6y ago
      > Then add on how many people show symptoms but its not severe enough to get tested. Earlier this week we took my son in because: 1. Our neighbors have recently recovered from Coronavirus 2. Our son had a cold / fever around the same time lasting several days 3. He had several days of diarrhea after the cold symptoms subsided I talked to my coworker whose wife is a doctor and he relayed the symptoms to her and she said it very well could be a mild coronavirus infection. We weren't concerned for his health because he's handled it just fine, but we figured it would be good to know in terms of avoiding spreading it to other people. So we called and set up an appointment. They got us in like an hour and half after we called. Got there and the doctor said, "Nope, no need for a test." At this point I'm extremely skeptical that the number counts are in any way accurate. Also I've lost faith in the "we're not doing enough testing" argument since we went and tried to get tested and they turned us away.
      - watwut 6y ago
        > Also I've lost faith in the "we're not doing enough testing" argument since we went and tried to get tested and they turned us away. That does not imply that there is enough testing. That just implies that your doctor or health care system is unwilling to test someone in your circumstances. "Not doing enough testing" is not referring to just test kids not being available, it is also referring to health system policies and willingness/unwilingness to test people.
        war1025 6y ago
        I guess to clarify, it has been my impression that the healthcare industry are the people telling us we are not doing enough testing. We attempted to get tested and they said no, not worth the bother. That seems contradictory to me.
        learc83 6y ago
        It depends on where you are. If you have a low enough case count and a well functioning health department that is doing contact tracing, then it's helpful to confirm that your kid is positive. If you're in an area where neither of those things apply then, for a child a test isn't going to change anything. It's not going to change their treatment. If it's positive they'll tell you to isolate, but if it's negative, there's a high enough false negative rate, and there are enough cases that it's still very likely they have it, so you'll still want to treat it like they do.
  - timr 6y ago
    Yes. The actual number, per the CDC, is probably 5-10x higher than the current confirmed infection count. https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/commercial-lab-surveys.html https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/comm... (fyi: they bury the lede on this page: you have to click through to their horribly slow interactive viewer widget to see the multiples.)
  - cma 6y ago
    Based on New York seropositivity, there would be a 5-6X multiplier on cases I believe. However that could change since they were test constrained when generating lots of those cases (downward?), and demographics of infected have changed (upward? younger may push multiplier higher as they are more asymptomatic and potentially get tested less).
- StevePerkins 6y ago
  > USA is currently at ~8M infections/recovered CONFIRMED cases. The total number of cases is probably 5-10x that. I live in the Deep South, and honestly I suspect that our curves have fallen simply due to a "limited" herd immunity effect (i.e. the groups of people most likely to catch COVID have already done so in large enough numbers). I certainly haven't observed any significant change in behaviors since the July peak, yet the numbers are falling like a rock regardless.
  - HarryHirsch 6y ago
    We know that coronaplague spreads through superspreading events, person-to-person transmission is wildly variable, most people don't infect anyone, but some give it to a dozen. You'd like to know if people are wearing masks at church or if family get-togethers are now outdoors.
    - StevePerkins 6y ago
      I think the common perception on HN, Reddit, etc is that COVID spread in the U.S. is primary a matter of conservative people flouting its seriousness. I understand the satisfying appeal of that picture. However, I'm looking at my local health department's ZIP-code-by-ZIP-code infection map of the metro area. And it seems almost entirely correlated with poverty, not privilege. Infection spread seems mostly due to "essential" workers continuing to work. That's a problematic thing to point out, because I don't think we can or will solve for that. But it's plain as day.
      - HarryHirsch 6y ago
        Yes, you'd say that the Red areas are on aggregate older, poorer and less likely to work from home. That said, at my regional college in the Deep South, case numbers have dropped noticeably since the beginning of term - instead of 30 cases every day we have now ten, and there have been remarkably few outbreaks at frathouses, all that despite no organized testing.
        deleted 6y ago
- eternalban 6y ago
  > infections/recovered This is a false binary state space. The implication here is that having "tested positive" is equivalent to having an "infection". An infection, by definition, is an alteration of the biological state of the entity with observable side-effects (symptoms). It is patently false to assert that "testing positive" for this virus is 100% indicative of an "infection". Further, "100M infections/recovered" implies that this infection can lead to "recovered" implying that the other alternative to recovere is a terminal/chronic condition. I guess this makes sense if we agree that many millions of "infected" immediately "recover" after testing positive, given that a substantial subset of those who "test positive" are "asymptomatic", reasonably understood as not-ill, not-sick, not-infected. Thus insta "recovery". My overall point here is that the permitted vocabulary of speaking and reasoning about this phenomena is inexplicably illiterate. Whether this permitted simplistic vocabulary of discourse is by design or a symptomatic of the state of humanity, the inevitable consequence is a degradation of analysis and sub-optimal solutions.
  - beervirus 6y ago
    No, that is not the definition of “infected.”
- e40 6y ago
  I wonder if this also means that only 35% of us need a vaccination to declare it over. I had previously read 60-70% were needed and that 35% of Americans get a flu shot. That depressed me. EDIT: seriously, downvoting this comment? Can't imagine why and would like to know.
  - tzs 6y ago
    I don't understand why more people do not get flu shots, unless they have no medical insurance and cannot afford the cost. It's not always effective, because they have to predict when they make it what strains of flu will be prevalent in the next flu season, and they don't always get that right, but in that case you are no worse off than if you had not gotten the vaccine. But when they do get it right, it can save you from getting the flu. That's certainly worth a few minutes getting it an a couple days with a sore arm. With a COVID vaccine, I doubt it will get anywhere near the same fraction of takers as the flu vaccine. 1. The anti-vaccine crowd probably won't take it. 2. The "COVID is no worse than a mild flu" crowd probably won't take it. Even if they do, it won't be at a higher rate than they take the flu vaccine. 3. The "COVID is a hoax" crowd probably won't take it. 4. A lot of the people who believe COVID is real and serious will probably be turned off if the approval seems to have involved politicians forcing approval over the objection of scientists who say it is not ready yet. (Especially if those politicians have also been pushing the "no worse than a mild flu" narrative).
    - dragonwriter 6y ago
      > With a COVID vaccine, I doubt it will get anywhere near the same fraction of takers as the flu vaccine. It will if closures are lifted but vaccination is made a requirement (either privately or by government mandate) for on-site work, schooling, etc. The flu vaccine is treated as primarily a personal preventive medical treatment; while it is encouraged for public as well as personal health reasons, there is no force put behind it. But it is quite possible, and there is plenty of precedent for, public health measures to be mandated (especially a conditional mandate, like for schools, work in particular conditions--including any public content or even on-premises work) and enforced.
- hammock 6y ago
  Well, we could get to 2MM faster if we opened everything up for the less-vulnerable populations (i.e. everyone under 50 without obesity or heart conditions) for whom the survival rate is above 99.99%. You might then be looking at 500k a day rather than 50k.
  - goalieca 6y ago
    This is roughly what is called for here by some of the leading experts: https://gbdeclaration.org/ https://gbdeclaration.org/
    - regularfry 6y ago
      These are not "some of the leading experts". https://www.wired.co.uk/article/great-barrington-declaration-herd-immunity-scientific-divide https://www.wired.co.uk/article/great-barrington-declaration...
      - goalieca 6y ago
        Wired? Seriously? I don’t even trust them for tech news. Here are the authors. They are well credentialed Dr. Martin Kulldorff, professor of medicine at Harvard University, a biostatistician, and epidemiologist with expertise in detecting and monitoring of infectious disease outbreaks and vaccine safety evaluations. Dr. Sunetra Gupta, professor at Oxford University, an epidemiologist with expertise in immunology, vaccine development, and mathematical modeling of infectious diseases. Dr. Jay Bhattacharya, professor at Stanford University Medical School, a physician, epidemiologist, health economist, and public health policy expert focusing on infectious diseases and vulnerable populations.
        regularfry 6y ago
        And I'm sure at some point one of them is going to publish an epidemiological model in support of their position, and not a press release. Until then, they're not even at Wired's level.
- ardy42 6y ago
  > At the current rate of +50K infections per day, that's 20 days per 1M infections, so we need 20 days * 92 = 5 years before we achieve herd immunity (best case, assuming no vaccines)? That doesn't seem right. I can't remember exactly where I heard it, but I believe robust herd immunity in human populations has never been achieved for a virus like this without the widespread use of a vaccine. Which makes sense, because there's evolutionary pressure on viruses to adapt, and so many diseases remained endemic and common until vaccines where introduced for them. Edit: in response to the dead reply: the Spanish Flu didn't disappear. It killed tens of millions (out of a much smaller world population) and persisted for decades as a seasonal flu. IIRC, it didn't get eclipsed by other strains until the 50s.
  - anoncake 6y ago
    It technically didn't disappear, but mutating to the level of regular seasonal flu is almost as good.
  - COVardsStayHome 6y ago
    So how did the Spanish Flu disappear?
- jackpeterfletch 6y ago
  This is fag packet math, so I'll spare any exact figures. But if the second wave data for the UK is anything to go by, confirmed cases vs actual cases was at _least_ 5x for the first wave. There obivously are other factors, but with increased testing that multiplier only climbs, bringing herd immunity numbers actually within reasonable grasp. I strongly suspect there have been similar effects in the US.
  - bigbubba 6y ago
    (People scribble on cigarette packages? Aren't those waxed cardboard or something? I wouldn't expect a pen to work well on those.)
    - pbhjpbhj 6y ago
      FWIW they almost certainly didn't write on a cigarette package in this instance ;o) It's just the name of that type of maths because people used to use whatever small, available, piece of paper was around - so cigarette packs some time ago (you definitely could write on them with a ballpoint pen (ie un bic). Getting tangential, napkins to me in the UK have always been cloth, and we have serviettes (a French word, meaning sheet IIRC) made of paper to wipe our mouths with. Our language gets more and more influenced by USA "English" usage, so perhaps youth would just call it a napkin. People do say 'paper napkin' but without the qualifier it's a fancy piece of cloth [to me].
      - mikelward 6y ago
        I can't decide whether to use the term cutlery (mainly UK) or silverware (mainly US). They're both inaccurate, especially when asking for plastic/disposable versions.
        PaulDavisThe1st 6y ago
        https://separatedbyacommonlanguage.blogspot.com/2008/09/stemware-and-other-wares.html https://separatedbyacommonlanguage.blogspot.com/2008/09/stem...
- mchusma 6y ago
  16% is a good estimate of US infection rate. https://covid19-projections.com/ https://covid19-projections.com/ (Excellent source during these times. Sad to see them deciding to stop moving forward but it's good for now).
- rst 6y ago
  This also assumes that acquired immunity from an infection is complete and permanent. Immunity to other coronaviruses decays over a year or two -- meaning that before the five years are up in your scenario, there would be a significant cohort of prior victims open to reinfection. See, e.g., https://www.nature.com/articles/s41591-020-1083-1 https://www.nature.com/articles/s41591-020-1083-1
  - sfblah 6y ago
    So, maybe that means by slowing the infection, what we're really doing is ensuring a neverending slow wave of infections ... forever? Maybe what normally happens with these kinds of viruses is they infect everyone then die out? And if you slow that, they never die out?
    - rst 6y ago
      No, it means that the expectation that "herd immunity" will be naturally reached, without an effective vaccine, is a pipe dream. Before vaccines, no population ever reached "natural herd immunity" for polio, which has similar R values; you need effective vaccines, effectively delivered, to get that result.
    - emodendroket 6y ago
      I don't think so. For instance, coronaviruses are among the causes of common cold. That one seems to have been with us for a while.
    - D_Alex 6y ago
      OTOH, a large number of infected people means a large pool of viruses to mutate into potentially re-infective strains.
- gpm 6y ago
  200k dead, infection fatality rate estimates seem to vary between 0.1 and 1%, so there should be at least 20m infections.
- autokad 6y ago
  No, we are undercounting the number of people who have it (asymptomatic or not) by a huge factor. at one point it was by a factor of 10, but I doubt that is still the case. This is why I watch florida like an eagle, because if it stops going up there we know we got a very good estimate to know when the top is. ~2.5-3% (730k/21.5m) of Florida has had it and it's slowed dramatically (use to be like 16k/day now down to 3). It feels reasonable that herd immunity starts slowing down the virus pretty fast somewhere around 25-30%. It seems reasonable it may come to a complete halt by 47%.
blakesterz 6y ago
I really struggle reading academic studies still... "Heterogeneity in contact structure and individual variation in infectivity, susceptibility, and resistance are key factors that reduce the disease-induced herd immunity levels to 34.2-47.5% in our models." I THINK that means, in addition to how infectious COVID is, and how susceptible and resistant people are in general, one of the other things that impact herd immunity is "contact structure" and it tends to be sort of limited. There seems to be plenty of "Heterogeneity in contact structure" studies done on many other things out there, so it looks like this is something that's already understood. If I understand it correctly, it means that most people have limited contacts, and while we all might be "6 degrees" from everyone else, we're not directly contacting all those people, and so that could help with herd immunity. So that maybe reduces the number from 74% to this 34-47% number, which better. Does that mean "Heterogeneity in contact structure" is different for people based on things like how often we go out, where we go, how we travel and where we live? e.g. a subway/bus trip in Manhattan, NY is different than driving alone in Manhattan, KS.
- SpicyLemonZest 6y ago
  Yeah, that's what it's referring to. People with more points of contact are both more likely to catch the virus and have a larger impact on herd immunity once they're immune.
  - maerF0x0 6y ago
    An example of applying such a concept: vaccinating healthcare workers ahead of otherwise isolated people. I presume many healthcare workers see orders of magnitude more people per day than average and those people are more likely to be sick (else why are they getting healthcare?) .
jupp0r 6y ago
Keep in mind that "herd immunity" isn't really immunity, it's the point at which Rt (the average number of people each infected person passes the infection on to) drops below 1.0 and the spread shrinks instead of growing. Rt is dependent on how people behave. When behavior changes, Rt can change as well. Each herd immunity level is thus dependent on health measures, which is why "reaching" herd immunity and then loosening up health measures won't work. Edit: removed wrong information on R0 that's not really essential to my point
- timr 6y ago
  R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. Rt is simply notation of an estimate of R0 at a particular time. Either way, you're correct that "herd immunity", as used here, means the point at which time the infection rate begins to decline, and this is conditional on population behaviors. If people mix more freely, the estimate changes. However, the observation that people don't mix uniformly still applies, even if they mix a bit more than they do now. To put it in a CS context, it's like debating the magnitude of the constant, when the algorithm has a fundamentally different asymptotic behavior.
  - jupp0r 6y ago
    > R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. From Wikipedia: In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted {\displaystyle R_{0}}R_{0} (pronounced R nought or R zero),[20] of an infection can be thought of as the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection. https://en.wikipedia.org/wiki/Basic_reproduction_number https://en.wikipedia.org/wiki/Basic_reproduction_number
    - timr 6y ago
      You can think of it that way, but we never know, in practice, what level of actual immunity exists in a population. In any case, it's not relevant to my point: R0 is a contextual number, always defined by empirical data. It's not a fixed feature of the virus.
streptomycin 6y ago
https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v2 https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v... was a similar study a couple months ago that estimated 10-20%, rather than the 34.2-47.5% in this paper. The bigger question is how long immunity lasts, which is still not known.
- nradov 6y ago
  Immunity isn't a binary condition which lasts for a certain length of time and then stops. It exists on a spectrum. The best evidence we have indicates that most recovered patients will retain a significant level of immunity for at least several years. https://www.jimmunol.org/content/early/2020/09/03/jimmunol.2000839 https://www.jimmunol.org/content/early/2020/09/03/jimmunol.2...
- rossdavidh 6y ago
  Tests this year on blood from people who had SARS in 2003, indicated that 17 years later they still had T-cell responses . On the other hand, coronaviruses which are experienced as "colds" apparently have a lot less retention of immune system recognition. Optimistic scenario is that the immune system is "smart" enough to recognize which infections are a big deal which must be remembered forever, and which are not. Pessimistic scenario is we got lucky with SARS, and may not with Covid-19.
nradov 6y ago
These models are fundamentally flawed in that they assume immunity or susceptibility are binary conditions. Based on recent research it appears a significant fraction of the population has at least limited immunity from prior exposure to other coronaviruses. They can still get infected but the immune system clears it more quickly and they tend to suffer fewer symptoms compared to immunologically naive patients. https://www.jci.org/articles/view/143380 https://www.jci.org/articles/view/143380 https://pubmed.ncbi.nlm.nih.gov/32978311/ https://pubmed.ncbi.nlm.nih.gov/32978311/
- vannevar 6y ago
  I believe this model accounts for such individual response: "Heterogeneity in contact structure and individual variation in infectivity, susceptibility, and resistance are key factors..." (emphasis added)
  - AstralStorm 6y ago
    In general, that's one of those anomalous diffusion problems. Unfortunately, there are too many parameters to estimate without simplifying the model. So the reasonable solution is to take a maximum expected value of each and you can still be wrong. Important data we do not know is chiefly how effective SARS aerosols are and at what range and time.
- gpm 6y ago
  Every model is wrong, some models are useful. Does this flaw make this model useless? On the flip side is it a useful approximation even if it's not completely accurate?
timr 6y ago
Gabriela Gomes was one of the first epidemiologists making this observation (as far back as May), and has found even lower thresholds (10-20%): https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v3 https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v... https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v2 https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v... https://www.medrxiv.org/content/10.1101/2020.09.26.20202267v1 https://www.medrxiv.org/content/10.1101/2020.09.26.20202267v...
- xadhominemx 6y ago
  Well 20% of NYC had COVID and we are currently seeing outbreaks in communities that have relaxed social distancing measures, so it seems obvious that her calculations are incorrect.
  - salmon30salmon 6y ago
    That’s part of the thesis of the article. Some populations mix more than others. In the mixing populations the threshold will be higher. In populations with limited mixing, lower. 20% of NYC can have the virus and the general level for herd immunity can still be what is postulated. NYC is incredibly dense compared to the rest of the USA and as such will naturally have more mixing and a higher threshold than say Topeka, Kansas
    - xadhominemx 6y ago
      The USA as a whole is already at ~10-15% and the rate of infections increased since late summer, and we are not even in flu season
      - timr 6y ago
        Just because the US average is X% doesn't mean that the every community in the whole country is X%. There's clearly heterogeneity in the data.
        6y ago
zests 6y ago
I appreciate this paper because I feel like every single article about "herd immunity" completely misses the mark and makes some rather poor assumptions. These assumptions are likely made because they make COVID seem like a bigger deal which sells more papers and gets more clicks. When an article discussing herd immunity assumes a completely homogeneous population I just shake my head and wonder how in the world this article got published.
Animats 6y ago
Whatever happened to large-scale antibody testing? You'd think that someone would be testing a few thousand random people each week to see how many people have been infected to date. That sort of thing was being done in the US back in April.[1][2] But it seems to have stopped. If you're going to talk about "herd immunity", you need that info to get anywhere. [1] https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v2 https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v... [2] https://abc7ny.com/coronavirus-testing-antibody-new-york-ny/6117634/ https://abc7ny.com/coronavirus-testing-antibody-new-york-ny/...
- dmurray 6y ago
  The antibody tests seemed to be consistently underestimating other measures of Covid-19 immunity, even conservative ones, so they're not considered as useful as we thought in April or May. It's possible the tests aren't sensitive enough, or immunity is largely based on T-cells (more expensive to test for) rather than antibodies [0], or antibodies for other coronaviruses confer some level of immunity, or something else we still don't understand. [0] https://www.eurekalert.org/pub_releases/2020-08/cp-mcc081720.php https://www.eurekalert.org/pub_releases/2020-08/cp-mcc081720...
- saalweachter 6y ago
  There was a recent study of dialysis patients: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)32009-2/fulltext https://www.thelancet.com/journals/lancet/article/PIIS0140-6... TLDR: "During the first wave of the COVID-19 pandemic, fewer than 10% of the US adult population formed antibodies against SARS-CoV-2, and fewer than 10% of those with antibodies were diagnosed."
  - Animats 6y ago
    That's for the month of July 2020, which is useful, but not enough. We need trend data for this.
    - nradov 6y ago
      The trends won't really tell you much as we get further into the pandemic. Just because someone lacks a detectible level of antibodies doesn't necessarily mean they are susceptible.
wodenokoto 6y ago
What is the end-game of "flattening the curve"? Is it: - everybody will eventually, but much later, get covid and become immune? - Keep the infected number low until a vaccine is developed? - Something else?

umvi 6y ago

So, according to this paper 34.2-47.5% of US citizens need immunity before the pandemic can be declared over? So best case scenario we can achieve herd immunity with roughly 100M infections/recovered. USA is currently at ~8M infections/recovered, so that means we are roughly 8% of the way to herd immunity (best case). At the current rate of +50K infections per day, that's 20 days per 1M infections, so we need 20 days * 92 = 5 years before we achieve herd immunity (best case, assuming no vaccines)? That doesn't seem right.

deleted 6y ago
[deleted]
zwischenzug 6y ago
Actual infection count is probably far higher than 8M, isn't it? That's just number of positive tests.
- seanalltogether 6y ago
  I thought I remembered reading early on that icelandic testing was showing that 50% of all people infected there showed no symptoms. Then add on how many people show symptoms but its not severe enough to get tested.
  - StevePerkins 6y ago
    Well, then add on the number of people who just don't get a test regardless. My child had a fever a few weeks ago, it was an ORDEAL finding a place to get him tested. You have to be quite motivated. If you're not sick enough to require hospitalization, and especially if you're un-insured and poor and don't want to pay a couple-hundred bucks out of pocket, then you'll probably just ride it out and never get tested. I'm sure this is the state of things for tens of millions of Americans.
    - learc83 6y ago
      >My child had a fever a few weeks ago, it was an ORDEAL finding a place to get him tested. You have to be quite motivated. That's because the test won't change anything. If it's positive, they'll tell you to isolate your kid. If it's negative, there's a high enough false negative rate that you'll still need to basically treat them like they have COVID (stay home and isolate).
      - AstralStorm 6y ago
        Incorrect. Not being treated early is likely a main factor between likelihood of medium to severe.vs no to mild symptoms, beyond immunity. And isolation of sick patient from viral reservoir (such as fomites and other asymptomatic sick) is known to be important too, as it changes the viral inoculum dose.
        learc83 6y ago
        Normal healthy children who don't develop a severe case aren't treated at all, so talking about early treatment is irrelevant. I literally just talked about this with a close family member who is a Children's ER doctor. >And isolation of sick patient from viral reservoir (such as fomites and other asymptomatic sick) is known to be important too, as it changes the viral inoculum dose. This isn't known to be important. If a person has been infected long enough that they are already symptomatic then "viral inoculum dose" is irrelevant.
  - war1025 6y ago
    > Then add on how many people show symptoms but its not severe enough to get tested. Earlier this week we took my son in because: 1. Our neighbors have recently recovered from Coronavirus 2. Our son had a cold / fever around the same time lasting several days 3. He had several days of diarrhea after the cold symptoms subsided I talked to my coworker whose wife is a doctor and he relayed the symptoms to her and she said it very well could be a mild coronavirus infection. We weren't concerned for his health because he's handled it just fine, but we figured it would be good to know in terms of avoiding spreading it to other people. So we called and set up an appointment. They got us in like an hour and half after we called. Got there and the doctor said, "Nope, no need for a test." At this point I'm extremely skeptical that the number counts are in any way accurate. Also I've lost faith in the "we're not doing enough testing" argument since we went and tried to get tested and they turned us away.
    - watwut 6y ago
      > Also I've lost faith in the "we're not doing enough testing" argument since we went and tried to get tested and they turned us away. That does not imply that there is enough testing. That just implies that your doctor or health care system is unwilling to test someone in your circumstances. "Not doing enough testing" is not referring to just test kids not being available, it is also referring to health system policies and willingness/unwilingness to test people.
      - war1025 6y ago
        I guess to clarify, it has been my impression that the healthcare industry are the people telling us we are not doing enough testing. We attempted to get tested and they said no, not worth the bother. That seems contradictory to me.
        learc83 6y ago
        It depends on where you are. If you have a low enough case count and a well functioning health department that is doing contact tracing, then it's helpful to confirm that your kid is positive. If you're in an area where neither of those things apply then, for a child a test isn't going to change anything. It's not going to change their treatment. If it's positive they'll tell you to isolate, but if it's negative, there's a high enough false negative rate, and there are enough cases that it's still very likely they have it, so you'll still want to treat it like they do.
- timr 6y ago
  Yes. The actual number, per the CDC, is probably 5-10x higher than the current confirmed infection count. https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/commercial-lab-surveys.html https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/comm... (fyi: they bury the lede on this page: you have to click through to their horribly slow interactive viewer widget to see the multiples.)
- cma 6y ago
  Based on New York seropositivity, there would be a 5-6X multiplier on cases I believe. However that could change since they were test constrained when generating lots of those cases (downward?), and demographics of infected have changed (upward? younger may push multiplier higher as they are more asymptomatic and potentially get tested less).
StevePerkins 6y ago
> USA is currently at ~8M infections/recovered CONFIRMED cases. The total number of cases is probably 5-10x that. I live in the Deep South, and honestly I suspect that our curves have fallen simply due to a "limited" herd immunity effect (i.e. the groups of people most likely to catch COVID have already done so in large enough numbers). I certainly haven't observed any significant change in behaviors since the July peak, yet the numbers are falling like a rock regardless.
- HarryHirsch 6y ago
  We know that coronaplague spreads through superspreading events, person-to-person transmission is wildly variable, most people don't infect anyone, but some give it to a dozen. You'd like to know if people are wearing masks at church or if family get-togethers are now outdoors.
  - StevePerkins 6y ago
    I think the common perception on HN, Reddit, etc is that COVID spread in the U.S. is primary a matter of conservative people flouting its seriousness. I understand the satisfying appeal of that picture. However, I'm looking at my local health department's ZIP-code-by-ZIP-code infection map of the metro area. And it seems almost entirely correlated with poverty, not privilege. Infection spread seems mostly due to "essential" workers continuing to work. That's a problematic thing to point out, because I don't think we can or will solve for that. But it's plain as day.
    - HarryHirsch 6y ago
      Yes, you'd say that the Red areas are on aggregate older, poorer and less likely to work from home. That said, at my regional college in the Deep South, case numbers have dropped noticeably since the beginning of term - instead of 30 cases every day we have now ten, and there have been remarkably few outbreaks at frathouses, all that despite no organized testing.
      - deleted 6y ago
eternalban 6y ago
> infections/recovered This is a false binary state space. The implication here is that having "tested positive" is equivalent to having an "infection". An infection, by definition, is an alteration of the biological state of the entity with observable side-effects (symptoms). It is patently false to assert that "testing positive" for this virus is 100% indicative of an "infection". Further, "100M infections/recovered" implies that this infection can lead to "recovered" implying that the other alternative to recovere is a terminal/chronic condition. I guess this makes sense if we agree that many millions of "infected" immediately "recover" after testing positive, given that a substantial subset of those who "test positive" are "asymptomatic", reasonably understood as not-ill, not-sick, not-infected. Thus insta "recovery". My overall point here is that the permitted vocabulary of speaking and reasoning about this phenomena is inexplicably illiterate. Whether this permitted simplistic vocabulary of discourse is by design or a symptomatic of the state of humanity, the inevitable consequence is a degradation of analysis and sub-optimal solutions.
- beervirus 6y ago
  No, that is not the definition of “infected.”
e40 6y ago
I wonder if this also means that only 35% of us need a vaccination to declare it over. I had previously read 60-70% were needed and that 35% of Americans get a flu shot. That depressed me. EDIT: seriously, downvoting this comment? Can't imagine why and would like to know.
- tzs 6y ago
  I don't understand why more people do not get flu shots, unless they have no medical insurance and cannot afford the cost. It's not always effective, because they have to predict when they make it what strains of flu will be prevalent in the next flu season, and they don't always get that right, but in that case you are no worse off than if you had not gotten the vaccine. But when they do get it right, it can save you from getting the flu. That's certainly worth a few minutes getting it an a couple days with a sore arm. With a COVID vaccine, I doubt it will get anywhere near the same fraction of takers as the flu vaccine. 1. The anti-vaccine crowd probably won't take it. 2. The "COVID is no worse than a mild flu" crowd probably won't take it. Even if they do, it won't be at a higher rate than they take the flu vaccine. 3. The "COVID is a hoax" crowd probably won't take it. 4. A lot of the people who believe COVID is real and serious will probably be turned off if the approval seems to have involved politicians forcing approval over the objection of scientists who say it is not ready yet. (Especially if those politicians have also been pushing the "no worse than a mild flu" narrative).
  - dragonwriter 6y ago
    > With a COVID vaccine, I doubt it will get anywhere near the same fraction of takers as the flu vaccine. It will if closures are lifted but vaccination is made a requirement (either privately or by government mandate) for on-site work, schooling, etc. The flu vaccine is treated as primarily a personal preventive medical treatment; while it is encouraged for public as well as personal health reasons, there is no force put behind it. But it is quite possible, and there is plenty of precedent for, public health measures to be mandated (especially a conditional mandate, like for schools, work in particular conditions--including any public content or even on-premises work) and enforced.
hammock 6y ago
Well, we could get to 2MM faster if we opened everything up for the less-vulnerable populations (i.e. everyone under 50 without obesity or heart conditions) for whom the survival rate is above 99.99%. You might then be looking at 500k a day rather than 50k.
- goalieca 6y ago
  This is roughly what is called for here by some of the leading experts: https://gbdeclaration.org/ https://gbdeclaration.org/
  - regularfry 6y ago
    These are not "some of the leading experts". https://www.wired.co.uk/article/great-barrington-declaration-herd-immunity-scientific-divide https://www.wired.co.uk/article/great-barrington-declaration...
    - goalieca 6y ago
      Wired? Seriously? I don’t even trust them for tech news. Here are the authors. They are well credentialed Dr. Martin Kulldorff, professor of medicine at Harvard University, a biostatistician, and epidemiologist with expertise in detecting and monitoring of infectious disease outbreaks and vaccine safety evaluations. Dr. Sunetra Gupta, professor at Oxford University, an epidemiologist with expertise in immunology, vaccine development, and mathematical modeling of infectious diseases. Dr. Jay Bhattacharya, professor at Stanford University Medical School, a physician, epidemiologist, health economist, and public health policy expert focusing on infectious diseases and vulnerable populations.
      - regularfry 6y ago
        And I'm sure at some point one of them is going to publish an epidemiological model in support of their position, and not a press release. Until then, they're not even at Wired's level.
ardy42 6y ago
> At the current rate of +50K infections per day, that's 20 days per 1M infections, so we need 20 days * 92 = 5 years before we achieve herd immunity (best case, assuming no vaccines)? That doesn't seem right. I can't remember exactly where I heard it, but I believe robust herd immunity in human populations has never been achieved for a virus like this without the widespread use of a vaccine. Which makes sense, because there's evolutionary pressure on viruses to adapt, and so many diseases remained endemic and common until vaccines where introduced for them. Edit: in response to the dead reply: the Spanish Flu didn't disappear. It killed tens of millions (out of a much smaller world population) and persisted for decades as a seasonal flu. IIRC, it didn't get eclipsed by other strains until the 50s.
- anoncake 6y ago
  It technically didn't disappear, but mutating to the level of regular seasonal flu is almost as good.
- COVardsStayHome 6y ago
  So how did the Spanish Flu disappear?
jackpeterfletch 6y ago
This is fag packet math, so I'll spare any exact figures. But if the second wave data for the UK is anything to go by, confirmed cases vs actual cases was at _least_ 5x for the first wave. There obivously are other factors, but with increased testing that multiplier only climbs, bringing herd immunity numbers actually within reasonable grasp. I strongly suspect there have been similar effects in the US.
- bigbubba 6y ago
  (People scribble on cigarette packages? Aren't those waxed cardboard or something? I wouldn't expect a pen to work well on those.)
  - pbhjpbhj 6y ago
    FWIW they almost certainly didn't write on a cigarette package in this instance ;o) It's just the name of that type of maths because people used to use whatever small, available, piece of paper was around - so cigarette packs some time ago (you definitely could write on them with a ballpoint pen (ie un bic). Getting tangential, napkins to me in the UK have always been cloth, and we have serviettes (a French word, meaning sheet IIRC) made of paper to wipe our mouths with. Our language gets more and more influenced by USA "English" usage, so perhaps youth would just call it a napkin. People do say 'paper napkin' but without the qualifier it's a fancy piece of cloth [to me].
    - mikelward 6y ago
      I can't decide whether to use the term cutlery (mainly UK) or silverware (mainly US). They're both inaccurate, especially when asking for plastic/disposable versions.
      - PaulDavisThe1st 6y ago
        https://separatedbyacommonlanguage.blogspot.com/2008/09/stemware-and-other-wares.html https://separatedbyacommonlanguage.blogspot.com/2008/09/stem...
mchusma 6y ago
16% is a good estimate of US infection rate. https://covid19-projections.com/ https://covid19-projections.com/ (Excellent source during these times. Sad to see them deciding to stop moving forward but it's good for now).
rst 6y ago
This also assumes that acquired immunity from an infection is complete and permanent. Immunity to other coronaviruses decays over a year or two -- meaning that before the five years are up in your scenario, there would be a significant cohort of prior victims open to reinfection. See, e.g., https://www.nature.com/articles/s41591-020-1083-1 https://www.nature.com/articles/s41591-020-1083-1
- sfblah 6y ago
  So, maybe that means by slowing the infection, what we're really doing is ensuring a neverending slow wave of infections ... forever? Maybe what normally happens with these kinds of viruses is they infect everyone then die out? And if you slow that, they never die out?
  - rst 6y ago
    No, it means that the expectation that "herd immunity" will be naturally reached, without an effective vaccine, is a pipe dream. Before vaccines, no population ever reached "natural herd immunity" for polio, which has similar R values; you need effective vaccines, effectively delivered, to get that result.
  - emodendroket 6y ago
    I don't think so. For instance, coronaviruses are among the causes of common cold. That one seems to have been with us for a while.
  - D_Alex 6y ago
    OTOH, a large number of infected people means a large pool of viruses to mutate into potentially re-infective strains.
gpm 6y ago
200k dead, infection fatality rate estimates seem to vary between 0.1 and 1%, so there should be at least 20m infections.
autokad 6y ago
No, we are undercounting the number of people who have it (asymptomatic or not) by a huge factor. at one point it was by a factor of 10, but I doubt that is still the case. This is why I watch florida like an eagle, because if it stops going up there we know we got a very good estimate to know when the top is. ~2.5-3% (730k/21.5m) of Florida has had it and it's slowed dramatically (use to be like 16k/day now down to 3). It feels reasonable that herd immunity starts slowing down the virus pretty fast somewhere around 25-30%. It seems reasonable it may come to a complete halt by 47%.

blakesterz 6y ago

I really struggle reading academic studies still... "Heterogeneity in contact structure and individual variation in infectivity, susceptibility, and resistance are key factors that reduce the disease-induced herd immunity levels to 34.2-47.5% in our models." I THINK that means, in addition to how infectious COVID is, and how susceptible and resistant people are in general, one of the other things that impact herd immunity is "contact structure" and it tends to be sort of limited. There seems to be plenty of "Heterogeneity in contact structure" studies done on many other things out there, so it looks like this is something that's already understood. If I understand it correctly, it means that most people have limited contacts, and while we all might be "6 degrees" from everyone else, we're not directly contacting all those people, and so that could help with herd immunity. So that maybe reduces the number from 74% to this 34-47% number, which better. Does that mean "Heterogeneity in contact structure" is different for people based on things like how often we go out, where we go, how we travel and where we live? e.g. a subway/bus trip in Manhattan, NY is different than driving alone in Manhattan, KS.

SpicyLemonZest 6y ago
Yeah, that's what it's referring to. People with more points of contact are both more likely to catch the virus and have a larger impact on herd immunity once they're immune.
- maerF0x0 6y ago
  An example of applying such a concept: vaccinating healthcare workers ahead of otherwise isolated people. I presume many healthcare workers see orders of magnitude more people per day than average and those people are more likely to be sick (else why are they getting healthcare?) .

jupp0r 6y ago

Keep in mind that "herd immunity" isn't really immunity, it's the point at which Rt (the average number of people each infected person passes the infection on to) drops below 1.0 and the spread shrinks instead of growing. Rt is dependent on how people behave. When behavior changes, Rt can change as well. Each herd immunity level is thus dependent on health measures, which is why "reaching" herd immunity and then loosening up health measures won't work. Edit: removed wrong information on R0 that's not really essential to my point

timr 6y ago
R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. Rt is simply notation of an estimate of R0 at a particular time. Either way, you're correct that "herd immunity", as used here, means the point at which time the infection rate begins to decline, and this is conditional on population behaviors. If people mix more freely, the estimate changes. However, the observation that people don't mix uniformly still applies, even if they mix a bit more than they do now. To put it in a CS context, it's like debating the magnitude of the constant, when the algorithm has a fundamentally different asymptotic behavior.
- jupp0r 6y ago
  > R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. From Wikipedia: In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted {\displaystyle R_{0}}R_{0} (pronounced R nought or R zero),[20] of an infection can be thought of as the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection. https://en.wikipedia.org/wiki/Basic_reproduction_number https://en.wikipedia.org/wiki/Basic_reproduction_number
  - timr 6y ago
    You can think of it that way, but we never know, in practice, what level of actual immunity exists in a population. In any case, it's not relevant to my point: R0 is a contextual number, always defined by empirical data. It's not a fixed feature of the virus.

streptomycin 6y ago

https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v2 https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v... was a similar study a couple months ago that estimated 10-20%, rather than the 34.2-47.5% in this paper. The bigger question is how long immunity lasts, which is still not known.

nradov 6y ago
Immunity isn't a binary condition which lasts for a certain length of time and then stops. It exists on a spectrum. The best evidence we have indicates that most recovered patients will retain a significant level of immunity for at least several years. https://www.jimmunol.org/content/early/2020/09/03/jimmunol.2000839 https://www.jimmunol.org/content/early/2020/09/03/jimmunol.2...
rossdavidh 6y ago
Tests this year on blood from people who had SARS in 2003, indicated that 17 years later they still had T-cell responses . On the other hand, coronaviruses which are experienced as "colds" apparently have a lot less retention of immune system recognition. Optimistic scenario is that the immune system is "smart" enough to recognize which infections are a big deal which must be remembered forever, and which are not. Pessimistic scenario is we got lucky with SARS, and may not with Covid-19.

nradov 6y ago

These models are fundamentally flawed in that they assume immunity or susceptibility are binary conditions. Based on recent research it appears a significant fraction of the population has at least limited immunity from prior exposure to other coronaviruses. They can still get infected but the immune system clears it more quickly and they tend to suffer fewer symptoms compared to immunologically naive patients. https://www.jci.org/articles/view/143380 https://www.jci.org/articles/view/143380 https://pubmed.ncbi.nlm.nih.gov/32978311/ https://pubmed.ncbi.nlm.nih.gov/32978311/

vannevar 6y ago
I believe this model accounts for such individual response: "Heterogeneity in contact structure and individual variation in infectivity, susceptibility, and resistance are key factors..." (emphasis added)
- AstralStorm 6y ago
  In general, that's one of those anomalous diffusion problems. Unfortunately, there are too many parameters to estimate without simplifying the model. So the reasonable solution is to take a maximum expected value of each and you can still be wrong. Important data we do not know is chiefly how effective SARS aerosols are and at what range and time.
gpm 6y ago
Every model is wrong, some models are useful. Does this flaw make this model useless? On the flip side is it a useful approximation even if it's not completely accurate?

timr 6y ago

Gabriela Gomes was one of the first epidemiologists making this observation (as far back as May), and has found even lower thresholds (10-20%): https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v3 https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v... https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v2 https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v... https://www.medrxiv.org/content/10.1101/2020.09.26.20202267v1 https://www.medrxiv.org/content/10.1101/2020.09.26.20202267v...

xadhominemx 6y ago
Well 20% of NYC had COVID and we are currently seeing outbreaks in communities that have relaxed social distancing measures, so it seems obvious that her calculations are incorrect.
- salmon30salmon 6y ago
  That’s part of the thesis of the article. Some populations mix more than others. In the mixing populations the threshold will be higher. In populations with limited mixing, lower. 20% of NYC can have the virus and the general level for herd immunity can still be what is postulated. NYC is incredibly dense compared to the rest of the USA and as such will naturally have more mixing and a higher threshold than say Topeka, Kansas
  - xadhominemx 6y ago
    The USA as a whole is already at ~10-15% and the rate of infections increased since late summer, and we are not even in flu season
    - timr 6y ago
      Just because the US average is X% doesn't mean that the every community in the whole country is X%. There's clearly heterogeneity in the data.
      - 6y ago

zests 6y ago

I appreciate this paper because I feel like every single article about "herd immunity" completely misses the mark and makes some rather poor assumptions. These assumptions are likely made because they make COVID seem like a bigger deal which sells more papers and gets more clicks. When an article discussing herd immunity assumes a completely homogeneous population I just shake my head and wonder how in the world this article got published.

Animats 6y ago

Whatever happened to large-scale antibody testing? You'd think that someone would be testing a few thousand random people each week to see how many people have been infected to date. That sort of thing was being done in the US back in April.[1][2] But it seems to have stopped. If you're going to talk about "herd immunity", you need that info to get anywhere. [1] https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v2 https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v... [2] https://abc7ny.com/coronavirus-testing-antibody-new-york-ny/6117634/ https://abc7ny.com/coronavirus-testing-antibody-new-york-ny/...

dmurray 6y ago
The antibody tests seemed to be consistently underestimating other measures of Covid-19 immunity, even conservative ones, so they're not considered as useful as we thought in April or May. It's possible the tests aren't sensitive enough, or immunity is largely based on T-cells (more expensive to test for) rather than antibodies [0], or antibodies for other coronaviruses confer some level of immunity, or something else we still don't understand. [0] https://www.eurekalert.org/pub_releases/2020-08/cp-mcc081720.php https://www.eurekalert.org/pub_releases/2020-08/cp-mcc081720...
saalweachter 6y ago
There was a recent study of dialysis patients: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)32009-2/fulltext https://www.thelancet.com/journals/lancet/article/PIIS0140-6... TLDR: "During the first wave of the COVID-19 pandemic, fewer than 10% of the US adult population formed antibodies against SARS-CoV-2, and fewer than 10% of those with antibodies were diagnosed."
- Animats 6y ago
  That's for the month of July 2020, which is useful, but not enough. We need trend data for this.
  - nradov 6y ago
    The trends won't really tell you much as we get further into the pandemic. Just because someone lacks a detectible level of antibodies doesn't necessarily mean they are susceptible.

wodenokoto 6y ago

What is the end-game of "flattening the curve"? Is it: - everybody will eventually, but much later, get covid and become immune? - Keep the infected number low until a vaccine is developed? - Something else?